There are many situations, such as in sports, transportation, on construction sights, and so on, where it is very difficult to discriminate between noise and sounds that a person wishes to hear. Resultingly, the noise effectively masks the sound and the sound is never heard. The noise may be ambient noise or may be as a result of air flow past the ears, which could be caused by wind or by motion of a person through the air, such as when riding a bicycle.
Since both ambient noise and noise from air flow past the ear contribute to the overall noise level experienced by a person, any situation that typically includes both of these sources of noise is a prime candidate for controlling the noise level around a person's ears. Further, in a situation where it is important that certain sounds be heard, the prevention and attenuation of noise and the amplification of these certain sounds is almost essential. Indeed, in some situations, it may be very dangerous to not hear certain sounds, and both ambient noise and air flow noise must be precluded from reaching the ear and the desired sounds should be amplified if possible.
One such situation occurs when a person is riding a bicycle. The noise experienced while riding a bicycle is caused largely by wind noise and also to some degree by ambient noise. It is also very important that certain sounds be heard, especially the sound of a vehicle approaching from the rear, since not hearing such sounds might cause a dangerous situation.
There are several million people in North America who regularly ride bicycles, whether for fun, for transportation purposes, for exercise, in athletic competition, or for whatever reason. While it is possible that in many places bicycles may be ridden on paths, lanes, or streets especially designated for bicycles, or at least where there are no motor vehicles, it is far more common that bicycles are ridden on roadways shared by motor vehicles. As such, it is nesessary that bicycles observe the rules of the road. In order to be within the rules of the road it is necessary that a cyclist ride on the same side of the road as a motor vehicle would travel on.
With having to share the road with cars, trucks, and the like, all of which are many times heavier and travel much faster than bicycles, safety becomes a very great concern for cyclists. This is especially true since any vehicle approaching a bicycle as it moves along the road would be approaching from the rear, which makes it very difficult to observe a motor vehicle as it approaches. Indeed, most motor vehicles go unnoticed until they are very close behind a cyclist. Typically, the first clue that a cyclist has that a vehicle is approaching very closely is the noise from the vehicle. Unfortunately, by the time a cyclist can hear or see a vehicle approaching, the vehicle is usually quite close behind or even directly beside the cyclist. Tests have shown that an average distance for being able to hear a vehicle approaching from behind is in the order of forty feet. This entire problem is exacerbated on roads where a cyclist may be travelling quickly, such as a highway or a country road, because of the increased wind noise in the cyclist's ear. Furthermore, on such roads, vehicles tend to travel faster and therefore the time between when they can first be heard and when they reach a cyclist is very minimal, in the order of one second or even half a second. Such a situation may be very dangerous given that the cyclist can not prepare for the approaching vehicle.
Such a situation could also occur in other types of activities such as running along roads, or even in unrelated events such as sports or construction sites where it may be nesessary to hear something from behind. Such sports might include sailing, football, hockey, bobsledding, and the like.